Laminoplasty Plates and Methods of Expanding the Spinal Canal

ABSTRACT

A method of expanding the spinal canal of a vertebra including inserting a bone anchor into a first lamina of the vertebra, cutting completely through the first lamina to create a space in the first lamina, cutting partially through a second, contra-lateral lamina of the vertebra to create a partial cut in the second lamina, engaging a first segment of a plate with the bone anchor, pivoting the bone anchor and the first lamina about the partial cut in the second lamina to increase the extent of the space in the first lamina, and connecting a second segment of the plate to a portion of the vertebra across the space from the first segment of the plate such that the plate spans the space and stabilizes the vertebra.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/609,251, filed on Oct. 30, 2009, which is herebyincorporated herein by reference.

BACKGROUND

The spinal cord can become compressed due to a variety of pathologicalconditions, thereby causing myelopathy and subsequent pain, weakness, orparalysis. One way to alleviate spinal cord compression is to expand thespinal canal, typically by displacing bone, such as the lamina, thatsurrounds the spinal cord. This procedure, generally referred to aslaminoplasty, typically involves making two types of cuts into thelamina, a complete osteotomy through the lamina on one side of the spineand a partial osteotomy, or “green stick”, on the contra-lateral lamina,which preserves the bottom cortex and creates a flexible hinge in thebone. This bridge of bone is then levered open about the hinge and fixedwith bone graft, plates, and screws. Screws are often driven into thissomewhat unstable mass of bone, which could pose a risk of injury to thespinal cord or an opportunity to fracture the green stick cut.

SUMMARY

Disclosed herein are improved laminoplasty plates and methods ofexpanding the spinal canal to decompress the spinal cord.

In one aspect, a method of expanding the spinal canal of a vertebra mayinclude inserting a bone anchor into a first lamina of the vertebra,cutting completely through the first lamina to create a space in thefirst lamina, cutting partially through a second, contra-lateral laminaof the vertebra to create a partial cut in the second lamina, engaging afirst segment of a plate with the bone anchor, pivoting the bone anchorand the first lamina about the partial cut in the second lamina toincrease the extent of the space in the first lamina, and connecting asecond segment of the plate to a portion of the vertebra across thespace from the first segment of the plate such that the plate spans thespace and stabilizes the vertebra.

In another aspect, a laminoplasty plate may include a first platesegment including a pair of spaced apart arms defining a slot that opensat a first end of the plate, a second plate segment including a firsthole for receiving a bone anchor, a central longitudinal axis of theplate extending from the first segment of the plate to the secondsegment of the plate, and a central plate segment interposed between thefirst plate segment and the second plate segment. The first platesegment and the second plate segment may lie in separate approximatelyparallel planes and the central plate segment may connect the firstplate segment and the second plate segment and may lie in a plane thatintersects the parallel planes.

BRIEF DESCRIPTION OF THE FIGURES

These and other features and advantages of the devices and methodsdisclosed herein will be more fully understood by reference to thefollowing detailed description in conjunction with the attached drawingsin which like reference numerals refer to like elements through thedifferent views. The drawings illustrate principles of the devices andmethods disclosed herein and, although not to scale, show relativedimensions.

FIG. 1 is a perspective view of an exemplary embodiment of alaminoplasty plate,

FIG. 2 is a side view of the laminoplasty plate of FIG. 1,

FIG. 3 is a top view of the laminoplasty plate of FIG. 1,

FIG. 4 is a front view of the laminoplasty plate of FIG. 1,

FIG. 5 is a perspective view of another exemplary embodiment of alaminoplasty plate;

FIG. 6 is a side view in cross section of a vertebra, illustratingcreating a cut through a first lamina of the vertebra,

FIG. 7 is a side view in cross section of the vertebra of FIG. 6,illustrating creating a partial cut through the second, contra-laterallamina of the vertebra,

FIG. 8 is a side view of the plate of FIG. 1, illustrating a bone graftconnected to the plate,

FIG. 9 is a partial side view in cross section of the vertebra of FIG.6, illustrating connecting the laminoplasty plate and bone graft of FIG.8 to the vertebra,

FIG. 10 is a side view in cross section of a vertebra, illustrating thelaminoplasty plate of FIG. 5 connected to the vertebra, and

FIG. 11 is a perspective view of another exemplary embodiment of alaminoplasty plate.

DETAIL DESCRIPTION OF EXEMPLARY EMBODIMENTS

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those of ordinary skill in the art will understand that thedevices and methods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e. to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

The terms “comprise,” “include,” and “have,” and the derivativesthereof, are used herein interchangeably as comprehensive, open-endedterms. For example, use of “comprising,” “including,” or “having” meansthat whatever element is comprised, had, or included, is not the onlyelement encompassed by the subject of the clause that contains the verb.

FIGS. 1-4 illustrate an exemplary embodiment of a laminoplasty plate 10.The exemplary laminoplasty plate includes a first plate segment 12including a pair of spaced apart arms 14A, 14B defining a slot 16 thatopens at a first end 18 of the plate 10. The exemplary plate 10 furtherincludes a second plate segment 20 including at least one hole, e.g.,first hole 22, for receiving a bone anchor and a central plate segment24 interposed between the first plate segment 12 and the second platesegment 20. A central longitudinal axis 26 of the plate 10 extends fromthe first plate segment 12 to the second plate segment 20. The firstplate segment 12 and the second plate segment 20, in the exemplaryembodiment lie in separate, approximately parallel planes, e.g., firstplane 28 and second plane 30, respectively, and the central platesegment 24 connects the first plate segment 12 and the second platesegment 20 and lies in a plane, e.g., third plane 32 that intersects theparallel planes.

Continuing to refer to FIGS. 1-4, the first plate segment 12 isconfigured to permit the first plate segment 12 to engage a previouslyimplanted bone anchor, as described in more detail below. In particular,the slot 16 is open at the first end 18 of the plate 10 such that thearms 14A, 14B may be positioned about the bone anchor, by, for example,sliding the arms 14A, 14B about the bone anchor thereby positioning atleast a portion of the bone anchor within the slot 16. In the exemplaryembodiment, the distance W between the arms 14A, 14B, e.g., the width ofthe slot 16, is greater than the diameter of the shank of the boneanchor. Each arm 14A, 14B, has a free end 34A, 34B and a fixed end 36A,36B which are connected to the first plate segment 12. Aninterconnecting surface 38 connects the fixed ends 36A, 36B of the arms14A, 14B and defines the base of the slot 16. In the exemplaryembodiment, the interconnecting surface 38 is arcuate in shape providingthe slot 16 with a generally U-shape.

The slot 16 may have a central slot axis 39 extending from the first end18 to the interconnecting surface 38. In the exemplary embodiment, thecentral slot axis 18 is coincident with the central longitudinal axis26. The first plate segment 12 may include one or more additional holes40 for receiving a bone anchor. The additional hole 40 or holes may bealigned along the central longitudinal axis 26 of the plate 10, suchthat, for example, the center of the hole 40 is positioned on centrallongitudinal axis 26, as in the exemplary embodiment. Alternatively, oneor more of the holes 40 may be offset from the central longitudinal axis26. For example, in the exemplary embodiment of a laminoplasty plate 200illustrated in FIG. 11, the hole 40 is positioned offset from thecentral longitudinal axis 26 and the hole 40 and slot 16 may be alignedalong an axis that is generally transverse to the central longitudinalaxis 26. The hole 40 may have a generally circular cross section, as inthe exemplary embodiment, or, alternatively, may have other suitableshapes. For example, the hole 40 may be in the form of elongated, closedslot having an elliptical cross section.

The second plate segment 20 may include one or more additional holes 42for receiving a bone anchor. The first hole 22 and the additional hole42 or holes may be aligned along the central longitudinal axis 26 of theplate 10, such that, for example, the center of the first hole 22 andthe additional hole 42 is positioned on central longitudinal axis 26, asin the exemplary embodiment. Alternatively, one or more of the holes 42may be offset from the central longitudinal axis 26. For example, in analternative exemplary embodiment of a laminoplasty plate 100 illustratedin FIG. 5 and the alternative exemplary embodiment of a laminoplastyplate 200 illustrated in FIG. 11, the first hole 22 and the additionalhole 42 are aligned along an axis 102 that is generally transverse tothe central longitudinal axis 26.

The first hole 22 and the additional hole 42 each may have a generallycircular cross section, as in the exemplary embodiment, or,alternatively, may have other suitable shapes. For example, the firsthole 22 and the additional hole 42 may be in the form of elongated,closed slot having an elliptical cross section. Such a configuration mayallow the plate 10 to be adjusted relative to the bone anchor positionedin the first hole 22 and the additional hole 42 along the longitudinalaxis of the closed slots defining the first and additional holes.

The central plate segment 24 may include an opening for receiving ananchor to connect a bone graft to the plate 10. In the exemplaryembodiment, the opening is an elongated, closed graft slot 44 having agenerally elliptical shape. The graft slot 44 has a central slot axis 46that, in the exemplary embodiment, is coincident with the centrallongitudinal axis 26 of the plate 10. The shape of the graft slot 44 canvary. For example, the graft slot 44 may be circular in shape. Moreover,multiple, spaced-apart graft slots 44 may be provided rather than asingle elongated slot.

The junction 50 between the first plate segment 12 and the central platesegment 24 and the junction 52 between the second plate segment 20 andthe central plate segment 24 may be constructed to permit bending of thefirst plate segment 50 at the junction 50 relative to the central platesegment 24 and bending of the second plate segment 20 at the junction 52relative to the central plate segment 24. To permit such bending, thejunction 50 and the junction 52 may have a reduced thickness compared toother segments of the plate 10.

The plate 10 may be constructed of any biocompatible material suitablefor implantation within the human body, including, for example,stainless steel, titanium and titanium alloys, and polymers, includingbiodegradable polymers.

Referring to FIGS. 6-10, an exemplary method of expanding the spinalcanal of a vertebra 70. The vertebra 70 to be treated, in the exemplarymethod, is a cervical vertebra, although the methods and platesdescribed herein may be used in vertebra throughout the spine. Theexemplary vertebra 70 includes a first lamina 72, first lateral mass 76,a second, contra-lateral lamina 74, a second, contra-lateral lateralmass 78, and a spinous process 80 between the first lamina 72 and thesecond lamina 74. A bulging portion of the disc 80 has entered thespinal canal 82 of the vertebra 70 and is impinging on the spinal cord84. The exemplary method will expand the spinal canal 82 such that thebulging disc 80 no longer impinges the spinal cord 84.

The exemplary method includes inserting a first bone anchor 60A into thefirst lamina 72 of the vertebra 70. The exemplary bone anchor 60Aincludes a proximal head 62 and a distal bone engaging shaft 64. Theproximal head 62 may have an increase diameter compared to the shaft 64and may include a drive feature to facilitate connection of aninstrument, such as a screwdriver, to the bone anchor 60A. The distalbone engaging shaft 64 may have a thread for engaging bone. In theexemplary method, the bone anchor 60A is inserted into the intact firstlamina 74, i.e., prior to cutting the first lamina 74. As a result, thefirst lamina 74 is stable during the process of inserting the first boneanchor 60A. Alternatively, the bone anchor may be inserted into thevertebra after the cutting the first lamina 74 and prior to the makingthe partial cut in the contra-lateral lamina.

Once the first bone anchor 60A is inserted, the first lamina 74 is cutcompletely through to create a space 86 in the first lamina 72, asillustrated in FIGS. 6 and 7. An instrument, such as a bur 66 or anyother bone cutting instrument, may be used to cut the first lamina 72.The cut and, thus, the subsequent space 86 may be made at the junctionof the first lamina 72 and the first lateral mass 76, as illustrated inFIG. 6.

The second, contra-lateral lamina 76 of the vertebra 70 may be partiallycut to create a partial cut 88 in the second lamina 76. An instrument,such as a bur 66 or any other bone cutting instrument, may be used topartially cut the second lamina 74. The partial cut 88, and thesubsequent hinge created by the partial cut 88 as discussed below, maybe made at the junction of the second lamina 74 and the second lateralmass 78, as illustrated in FIG. 7. The amount of bone removed during thepartially cutting is preferably sufficient to create a green-stickfracture and the deep cortex is preferably preserved to prevent acomplete fracture of the second lamina 74.

After creation of the partial cut 88, the first lamina 72 may be pivotedabout the partial cut 88 in the second lamina 76 with the partial cut 88acting as a hinge. The effect of this pivoting operation is to increasethe extent of the space 86 in the first lamina 72, e.g., the distancebetween the first cut edge 90 and the second cut edge 92, and to expandthe spinal canal 82, thereby decompressing the spinal cord 84. Thepivoting of the first lamina 72 may be accomplished by grasping in thefirst bone anchor 60A and using the first bone anchor 60A to pivot thefirst lamina 72. An instrument, such as a forceps or the like, may beused to grasp the first bone anchor 60A. Once the instrument grasps thebone anchor 60A, the instrument may be manipulated to pivot the firstbone anchor and, thus, the first lamina 72. Alternatively, the surgeonmay grasp the bone anchor 60A with his hand to pivot the first lamina72.

A laminoplasty plate may be attached to the first vertebra 70 tostabilize the first lamina 72 relative to the first lateral mass 76after expansion of the spinal canal 82. The laminoplasty plate maybridge the space 86 by connecting at one end to the first lamina 72 andat another end to the lateral mass 76. The laminoplasty plate may beconnected to the first lamina 72 and the first lateral mass 76 by boneanchors. Although the method described below will describe the use ofthe exemplary laminoplasty plate 10, other laminoplasty plates,including exemplary laminoplasty plate 100, may be utilized to stabilizethe vertebra 70.

In one exemplary method, a laminoplasty plate, such as laminoplastyplate 10 described above, may be connected to the vertebra 70 prior topivoting of the first lamina 72. For example, the first segment 12 ofthe plate 10 may be engaged with the first bone anchor 60A prior topivoting the first lamina 72 to expand the spinal canal 82. The firstportion 12 of the plate 10 may be engaged to the first bone anchor 60Aby sliding the arms 14A, 14B about the distal shaft 64 of the boneanchor 60A to position the bone anchor 60A within the slot 16. Once thebone anchor 60A is positioned within the slot 16, the bone anchor 60Amay be advanced further into the first lamina 72 to compress theproximal head 62 of the bone anchor 60A against the top surface of theplate 10. This final tightening of the first bone anchor 60A may occurbefore or after the connection of the second plate segment 20 to thevertebra 70.

Once the first segment 12 of the plate 10 is connected to the firstlamina 72, the plate 10 may be manipulated to cause the first boneanchor 60 and the first lamina 72 to pivot about the partial cut 88. Theplate 10 may be manipulated by hand by the surgeon or may be manipulatedby an instrument, such as, for example, a forceps, plate holder, or thelike. An exemplary plate holder is described in commonly owned,co-pending U.S. Patent Application Publication No. U.S. 2011/0106087 A1,entitled “Bone Plate Holder” concurrently filed herewith, which isincorporated herein by reference.

In alternative methods, the laminoplasty plate may be connected tovertebra 70, by, for example, engaging the plate 10 to the first boneanchor 60, after the first lamina 72 has been pivoted to expand thespinal canal.

The second segment 20 of the plate 10 may be connected to a portion ofthe vertebra 70 across the space from the first segment 12 of the plate10 such that the plate 10 spans the space 86 and stabilizes the vertebra70. For example, the second segment 20 of the plate 10 may be connectedto the first lateral mass 76, as illustrated in FIG. 9. The secondsegment 20 may be connected to the first lateral mass 76 by insertingbone anchors, for example, bone anchor 60B, through hole 22 and throughhole 42 of the second plate segment 20 and into the first lateral mass76. A drill 96 may be used to provide a hole within the first lateralmass 76 for receiving a bone anchor.

A second bone anchor, e.g, a bone anchor 60C, may be inserted throughhole 40 and into the first lamina 72 to further secure the first platesegment 12 to the first lamina 72. The second bone anchor 60C may beinserted through the first plate segment 12 and into the first lamina 72after the first lamina 72 is pivoted about the partial cut 88 or afterthe second plate segment 20 is connected to the vertebra. Alternatively,the second bone anchor 60C may be inserted through the first platesegment 12 and into the first lamina 72 before the first lamina 72 ispivoted about the partial cut 88.

In certain embodiments, a bone graft 108 may be positioned within theexpanded space 86 to facilitate fusion of the first lamina 72 across thespace 86. The bone graft 108 may be allograft or autograft and may beconnected to the laminoplasty plate prior to positioning within thespace 86. For example, the bone graft 108 may be connected to thecentral segment 42 of the laminoplasty plate 10 or the central segment24 of the laminoplasty plate 100 with a bone anchor, e.g. bone anchor60D, positioned through graft slot 44 and into the bone graft 108, asillustrated in FIG. 8. The bone graft 108 may have a first end 110 and asecond end 112 configured to engage the first cut edge 90 and the secondcut edge 92. In the exemplary embodiment, for example, the first end 110and the second end 112 each include a notch 114A, 114 b into which arespective one of the first cut edge 90 and the second cut edge 92 maybe seated.

The bone graft 108 may be connected to the laminoplasty plate using aninstrument that holds the bone graft 108 relative to the plate duringinsertion of the bone anchor 60D. An exemplary instrument is describedin commonly owned, co-pending U.S. Patent Application Publication No.U.S. 2011/0106084 A1, entitled “Bone Graft Loading Instruments andMethods of Connecting a Bone Graft to a Bone Plate” concurrently filedherewith, which is incorporated herein by reference.

FIG. 9 illustrates exemplary laminoplasty plate 10 connected to a bonegraft 108 and the bone graft 108 positioned in the expanded space 86.The spinal canal 82 of the vertebra 70 is expanded to decompress thespinal cord 84 and the laminoplasty plate 10 stabilizes the expandedvertebra 70.

In certain exemplary embodiments, the method of expanding the spinalcanal of a vertebra may be completed without a bone graft. In suchcases, the laminoplasty plate may be connected to the vertebra withoutthe bone graft. For example, FIG. 10 illustrates exemplary laminoplastyplate 100 connected to the first lamina 72 and the first lateral mass 76and spanning the expanded space 86. The spinal canal 82 of the vertebra70 is expanded to decompress the spinal cord 84 and the laminoplastyplate 100 stabilizes the expanded vertebra 70.

The exemplary method may be used to treat multiple vertebrae in a singleprocedure. For example, the spinal canal of two or more adjacentvertebra may be expanded and laminoplasty plates may be engaged to eachvertebra using the methods described above.

While the devices and methods of the present invention have beenparticularly shown and described with reference to the exemplaryembodiments thereof, those of ordinary skill in the art will understandthat various changes may be made in the form and details herein withoutdeparting from the spirit and scope of the present invention. Those ofordinary skill in the art will recognize or be able to ascertain manyequivalents to the exemplary embodiments described specifically hereinby using no more than routine experimentation. Such equivalents areintended to be encompassed by the scope of the present invention and theappended claims.

1. A laminoplasty plate comprising: first plate segment including a pairof spaced apart arms defining a slot that opens at a first end of theplate, a second plate segment including a first hole for receiving abone anchor, a central longitudinal axis of the plate extending from thefirst segment of the plate to the second segment of the plate, a centralplate segment interposed between the first plate segment and the secondplate segment, the first plate segment and the second plate segmentlying in separate approximately parallel planes and the central platesegment connecting the first plate segment and the second plate segmentand lying in a plane that intersects the parallel planes.
 2. Thelaminoplasty plate of claim 1, wherein the first plate segment includesa first hole for receiving a bone anchor.
 3. The laminoplasty plate ofclaim 2, wherein the first hole in the first plate segment has a centerthat lies on the central longitudinal axis of the plate.
 4. Thelaminoplasty plate of claim 2, wherein the second plate segment includesa second hole and the first hole and the second hole are aligned alongthe central longitudinal axis of the plate.
 5. The laminoplasty plate ofclaim 2, wherein the second plate segment includes a third hole and thesecond hole and the third hole are aligned along an axis transverse tothe central longitudinal axis.
 6. The laminoplasty plate of claim 1,wherein the central plate segment includes an opening for receiving ananchor to connect to a bone graft.
 7. The laminoplasty plate of claim 6,wherein the opening in the central plate segment is an elongated slothaving a slot axis that is coincident with the central longitudinal axisof the plate.
 8. The laminoplasty plate of claim 1, wherein the slot inthe first plate segment has a slot axis that is coincident with thecentral longitudinal axis of the plate.
 9. A laminoplasty platecomprising: first plate segment including a pair of spaced apart armsdefining a slot that opens at a first end of the plate, a second platesegment including a second hole for receiving a bone anchor and a thirdhole for receiving a bone anchor, a central longitudinal axis of theplate extending from the first segment of the plate to the secondsegment of the plate, the slot in the first plate segment having a slotaxis that is coincident with the central longitudinal axis of the plate,the first plate segment including a first hole for receiving a boneanchor, the first hole, the second hole, and the third hole each havinga center that lies on the central longitudinal axis of the plate, and acentral plate segment interposed between the first plate segment and thesecond plate segment, the first plate segment and the second platesegment lying in separate approximately parallel planes and the centralplate segment connecting the first plate segment and the second platesegment and lying in a plane that intersects the parallel planes. 10.The laminoplasty plate of claim 9, wherein the central plate segmentincludes an opening for receiving an anchor to connect to a bone graft.11. The laminoplasty plate of claim 10, wherein the opening in thecentral plate segment is an elongated slot having a slot axis that iscoincident with the central longitudinal axis of the plate.
 12. Alaminoplasty plate comprising: first plate segment including a pair ofspaced apart arms defining a slot that opens at a first end of theplate, a second plate segment including a second hole for receiving abone anchor and a third hole for receiving a bone anchor, a centrallongitudinal axis of the plate extending from the first segment of theplate to the second segment of the plate, the slot in the first platesegment having a slot axis that is coincident with the centrallongitudinal axis of the plate, the first plate segment including afirst hole for receiving a bone anchor, the first hole in the firstplate segment having a center that lies on the central longitudinal axisof the plate, the second hole and the third hole each having a centerthat lies on an axis that is perpendicular to the central longitudinalaxis of the plate, and a central plate segment interposed between thefirst plate segment and the second plate segment, the first platesegment and the second plate segment lying in separate approximatelyparallel planes and the central plate segment connecting the first platesegment and the second plate segment and lying in a plane thatintersects the parallel planes.
 13. The laminoplasty plate of claim 12,wherein the central plate segment includes an opening for receiving ananchor to connect to a bone graft.
 14. The laminoplasty plate of claim13, wherein the opening in the central plate segment is an elongatedslot having a slot axis that is coincident with the longitudinal axis ofthe plate.